This invention broadly relates to apparatus for vacuum contact reproduction. In particular the invention relates to such an apparatus wherein an extremely high evacuation potential, provided by a unique master vacuum system, is selectively applied to the respective evacuation chambers of plural vacuum contact printers to minimize the time required to effect intimate, non-distortional, contact between a photosensitive material and a transparency to be reproduced thereon. Included in the invention are automatic vacuum and exposure controls for independently controlling selective reproduction at each of the vacuum contact printers.
In contact reproduction, to produce high resolution, it is imperative that a transparency to be duplicated be securely drawn into, and maintained in, close contact with the sensitized material for exposure. Currently, the most commonly used device, the so-called vacuum contact printer, employs a vacuum frame in which the drawing of a vacuum forces the transparency into very close contact with the photosensitive material.
Other known devices utilize mechanical means to mechanically urge the materials into contact. Still other devices achieve close contact by employing mechanical means in combination with vacuum means.
While apparatus which is representative of these latter two types of prior art devices are effective, particularly when used in integrated circuit manufacture, they necessarily include complex mechanisms and associated complex controls which are not only costly to manufacture, but susceptible to operational fatigue and malfunction. Such devices are also not well adapted to versatile usage, particularly when the dimensions of the work pieces vary between successive operations.
The above mentioned prior art vacuum frames generally include a rubber blanket, which is disposed upon a support surface, a transparent cover, pivotally connected to the support surface for sealed engagement therewith, and a vacuum pump. In operation, the cover is disengaged, the transparency and photosensitive material are inserted, the cover is then closed, and the vacuum pump is activated, drawing the transparency and photosensitive material into close contact between the cover and rubber blanket.
Distinct operational disadvantages have been encountered when practicing duplication with such vacuum frames. Since the vacuum must be released to permit retrieval of the exposed work piece, each successive operation necessitates redrawing a vacuum from atmospheric pressure. Typically, the time required for the vacuum pump to draw a vacuum sufficient to closely contact the transparency and photosensitive material, the so-called draw-down, is on the order of several minutes. Since, for high resolution reproduction, it is imperative that exposure occur only while the photosensitive material transparency are in close contact, complete draw-down must be achieved prior to activating the exposure mechanism.
The known method of assuring complete draw-down requires the operator to make a visual scan, through the cover element of the vacuum frame, to detect the presence of air pockets or other distortion producing irregularities between the sensitized material and the transparency. This procedure requires, not only that the operator possess a high degree of skill in detecting the presence of such anomalies, but also, that he necessarily estimate the time required for complete draw-down. If the operator does not possess the requisite skill, or is inattentive during the several minutes required for draw-down, significant production time may be wasted. In practicing the prior art devices which employ this method, it is not uncommon for the entire process of draw-down and visual scan to take between five and ten minutes of operator time. Such time delays detrimentally affect overall production efficiency, especially where such delays are compounded in the production of a finished work-piece through multiple exposures, as, for example, in the production of composite printing films from color separated half-tone and line films.
Other prior art devices have reduced this problem by providing automatic control of the draw-down process, thus eliminating the guesswork involved in achieving the requisite state of evacuation. Such devices commonly employ a pressure responsive switch, which is associated with the vacuum pump, and which detects a predetermined level of low pressure in the vacuum frame and, thereupon, enables the exposure mechanism. While these systems have satisfactorily minimized direct operator involvement, they have not reduced the time period of several minutes that is required to achieve complete draw-down.
By contrast, the present invention not only eliminates direct operator assistance in determining complete draw-down but also significantly reduces the time required for such draw-down to approximately thirty (30) seconds or less. This is accomplished by providing a unique master vacuum system that is capable of applying an extremely high evacuation potential to the respective evacuation chambers of each of the plural vacuum contact printers. This evacuation potential is such as to guarentee that a fine end vacuum will be rapidly and uniformly developed within a given evacuation chamber during each successive operation. Because of such assurance of uniform and complete draw-down, the prior art needs for visual scanning and/or pressure responsive switching are totally obviated by the present invention. As well, the availability and predictability of such rapid draw-down allows the utilization of a simple control network operable upon time based parameters only. The control network, thus, is well adapted to construction from digital components. Such construction affords both reliability and manufacturing economy.